It’s a gorgeous music discovery machine:
When Twitter opened up its #Music app to everyone on Thursday, it was the strongest sign yet that the social-networking giant is aiming to become a media machine that dominates popular entertainment channels. … At the heart of Twitter #Music is a discovery engine. Users can see charts of the most popular songs on Twitter — sampling or listening to them via iTunes, Rdio, and Spotify as they go — as well as get a sense of the songs their Twitter friends are sharing. At the same time, users can see the songs their favorite artists are sharing, as well as the people they follow. All in all, the idea is to make it as easy as possible to find new music.
A good overview: